Method for sanding surfaces on items

ABSTRACT

With sanding or sanding machines with rotating sanding tools comprising sanding segments which are rotated in mutually opposite directions, according to the invention a more uniform sanding result and uniform wear on the tools is achieved with a method whereby the tools ( 10 ) which are rotated in the direction like a roller are rotated in the direction like a roller are rotated slightly faster than are the tools ( 1 ) which are rotated in the opposite direction. The necessary increase in speed has shown to be around 7%, since the individual segments under the increased influence of the centrifugal force will thus obtain the same sanding pressure and herewith a uniform sanding effect for all of the sanding tools regardless of their direction of rotation to thee item.

PRIOR ART TECHNIQUE

The invention concerns a method for the sanding of surfaces on items bymeans of tools which consist of sanding segments which extend radiallyfrom a core in the formation of a cylindrical sanding tool, said toolbeing rotated around an axis of rotation which extends substantiallyparallel with the surface on the item, so that under the influence ofcentrifugal force the individual sanding segments exert a sandingpressure against the surface of the item, and where there are mountedseveral of such tools which are rotated in mutually opposite directionswhile at the same time being moved in relation to the item, or where theitem is moved in relation to the sanding tools.

The sanding of surfaces by means of such tools is used especially forthe processing of wooden items whose surfaces must be smooth.

Similarly, in connection with lacquered surfaces, the sanding can beused with advantage as intermediate sanding between lacquerapplications.

Moreover, the method can be used for the cleaning of metal surfaces,where the sanding also serves to deburr the edges so that both aneffective and uniform deburring is achieved.

Finally, the method can be used for items of plastic where, for example,the surface must be ground with the object of removing fraze and/or forsubsequent surface treatment.

Machines are known for the execution of such a method. For example, fromthe description of DK Patent 156.703, a machine is known for the sandingof wooden items, and which is provided with six sanding rollers in atool which rotates in such a manner that adjacent rollers are rotated inopposite directions during the turning of the tool over the item.

The individual rollers are rotated at the same speed, i.e. the rollerswhich rotate clockwise and the rollers which rotate counter-clockwiseduring the turning of the tool over the item all rotate at the samespeed.

However, there hereby arises a small difference in the sanding effect ofthe individual sanding elements, the reason being that because of thedifferences in the relative speeds, the individual sanding segments willhave different contact pressure, sanding pressure, against the surfaceof the item.

The sanding elements on the tools rotating in the manner like a rollerwill namely be fed a little slower over the item, and herewith have arelatively lower sanding effect than the corresponding sanding elementson the tools which rotate in the opposite direction, in that therelative sanding speed of these is higher and the sanding effecttherefore greater than that of the tools which rotate like a roller.

This difference in effect results not only in a non-uniform sanding ofthe surface, but also a non-uniform wear on the sanding elements.

From DK 9300243 Y6 there is known a pass-through sanding machine withsanding tools which have variable speeds of rotation. The object of thisis to be able to mount sanding tools successively with different sandingaggressiveness, in that the speed of the individual tools can be set inaccordance with their aggressiveness.

THE OBJECT OF THE INVENTION

It is the object of the invention to remedy the disadvantages anddrawbacks of the known methods, and this is achieved according to theinvention when the sanding tool which moves in the rolling directionover the item is rotated more quickly than the tool which moves in theopposite direction over the item is rotated.

According to the invention, by simply rotating the tools which rotate inthe direction like a roller faster than the tools which are rotated inthe opposite direction, there can hereby be achieved a completelyuniform sanding effect by all of the sanding segments regardless oftheir direction of rotation.

In a surprisingly simple manner, there is hereby achieved a completelyperfect sanding result, completely without any variation in the sandingby the individual sanding tools, and with a completely uniform wear onthe sanding elements as a result.

Moreover, a uniform physical loading of the item on the belt isachieved, in that there will be uniform side effects on the item fromboth the tools which rotate like a roller and those which rotate in theopposite direction.

To this can be added that in step with the wear, the speed of rotationof the sanding tools can gradually be increased to compensate for thereduced sanding effect while avoiding the hitherto-known simultaneousincrease in non-uniformity in the sanding, which occurs particularly dueto the increased heating-up of the sanding tools which rotate in theopposite direction. This is especially important for the sanding ofmetal plate, where variations in temperature will give rise to tensionsand deformations in the metal plate.

As disclosed in claim 2, by letting the tools which rotate in thedirection like a roller rotate 13% faster than the tools rotating in theopposite direction, theoretically a completely uniform sanding pressureis achieved for both types of sanding tools, but since the centrifugalforce plays a role at the relatively high speeds of rotation, anincrease of only 7% in the speed of the tools rotating in the rollingdirection has shown to provide the most uniform sanding result, andherewith a correspondingly uniform wear on the sanding elements.

Due to the progressiveness of the centrifugal force, the increase inrotation of 7% will correspond to the theoretical compensation of 13%for achieving a uniform sanding force or sanding pressure.

THE DRAWING

The invention will be described in more detail in the following sectionwith reference to the drawing, where

FIG. 1 is a perspective view of a sanding tool during operation,

FIG. 2 shows a sanding tool rotating in the direction like a roller seenfrom the outside, and

FIG. 3 shows a sanding tool rotating in the opposite direction,similarly seen from the outside, both during operation.

DESCRIPTION OF THE METHOD

In FIG. 1 there is shown an example of a sanding tool which partlycomprises three cylindrical sanding tools 10 which are rotatedcounter-clockwise seen from the outside end, and as shown in FIG. 2, andpartly three sanding tools 1 which are rotated clockwise seen from theoutside end, and as shown in FIG. 3.

The sanding tools can consist of disks cut from sheet material and whichare provided with incisions extending radially outwards for theformation of segmented sanding elements 2. The individual sanding disksare provided with a hole around the centre axis so that they can bemounted on an axle 3 by being pushed on to said axle and tightened toform a sanding tool 1, 10

The six rotation axles 3 are housed in a drive 11 mounted on a turningshaft 12 which can turn the drive 11, and therewith the tools 1, 10,around over the item 4 in a turning movement which extends parallel tothe surface of the item.

When the tools 1, 10 are thus turned, as indicated by the arrow 6, theindividual axles 3 with the tools 1, 10 are rotated so that the threetools 10 are rotated in the direction like a roller, as indicated by thearrow 8, while the remaining tools 1 are rotated in the oppositedirection, as indicated by the arrow 9.

During the sanding, the individual tools 1, 10 are rotated on theiraxles 3 while at the same time they are turned over the item 4 by theshaft 12 in a turning movement 6.

In order for the whole of the item to be swept by the tools, it can bemoved in relation to the tools, e.g. on a not-shown transport plane, orthe tools can be moved over the item. Alternatively, this can beeffected by a combination of movements, i.e. where both the item and thetools are moved in relation to one another.

In order to achieve a perfect sanding result, according to the inventionthe three tools 10 rotating in the rolling direction must be rotatedslightly faster than the three tools 1 rotating in the oppositedirection. This is indicated in the drawing by means of arrows 8 and 9,the length of which indicates the difference in the speed of rotation.

An example of such a sanding tool can have an outer tool diameter of 300mm, a speed of rotation of 1,000 rpm in the oppositely directedrotation, and a speed of rotation of 1,070 rpm in the rolling direction,i.e. a 7% increase in speed in relation to the speed in the oppositedirection.

The theoretical difference between the relative speeds of the tools inthe rolling direction and the opposite direction over the item is 13%,but because of the increased influence of the centrifugal force on thesanding segments during the increase in speed, it is thus only necessaryto increase the speed of rotation by 7%. There is thus hereby achievedthe same relative sanding speed and herewith sanding pressure over theitem for all of the segments on the tools.

The difference is shown in FIGS. 2 and 3, and it is seen that the tool10 rotating in the rolling direction rotates slightly faster than thetool 1 rotating in the opposite direction, whereby this resultingsanding effect becomes uniform due to the uniform sanding movements ofthe individual sanding elements.

There is hereby achieved a uniform sanding result, in that at no timewill there be any variation on the surface 5 of the item 4.

Further to this improvement in the sanding result, a uniform wear on thesanding elements 2 will also be achieved, the reason being that theseare now loaded to the same degree by the uniform sanding effect. Thelifetime of the tools thus becomes the same for all of the tools, andthe changing of the sanding disks on all of the tools can therefore beeffected at the same time.

It is naturally an advantage that the sanding tools can be replaced atthe same time, and not when only half of them are worn down.

Since the load on the items is more uniform, the securing effect on theconveyor can be reduced to the average load, whereby the consumption ofpower by the vacuum conveyor can be considerably reduced.

Moreover, the uniform wear on the sanding elements will enable thesanding effect to be adjusted, which will result in a uniform result,and will not like the known methods give rise to an increased sandingeffect for the tools rotating in the opposite direction with asubsequent non-uniform heating-up.

The method is described in connection with a sanding tool as shown inFIG. 1, but the same method can be executed with sanding machines ofother constructions, merely providing that they comprise tools which arerotated in different directions. It is thus possible for the sandingresult for all such sanding tools to be improved by changing the speedat which their tools are rotated.

What is claimed is:
 1. Method for sanding a surface on at least one itemcomprising using sanding tools in a form of a cylindrical sanding toolwhich consists of sanding segments extending radially from a core,rotating each sanding tool around an axis of rotation which extendssubstantially parallel with the surface on the item, so that under aninfluence of a centrifugal force, the sanding segments exert a sandingpressure against the item surface, and mounting the sanding tools whichare rotated in mutually opposite directions while at the same time beingmoved in relation to the item, or the item is moved in relation to thesanding tools, wherein a first sanding tool (10), which is moved (7)while rotating in one direction over the item (4), is rotated faster (8)than is a second sanding tool (1) which is moved (7) while rotating inan opposite direction (9) over the item (4).
 2. Method according toclaim 1, wherein to compensate for a difference in sanding pressure, aspeed of rotation (8) of the first sanding tool (10) is at a maximum 13%and preferably 7% higher than a speed of rotation (9) for the secondsanding tool (1) rotating in the opposite direction.